When a Windows NT client connects to a Windows 2000 Server running Terminal Services, the client is issued a Terminal Services Client Access License token for every user of the computer.
This problem will occur if the Users group does NOT have Full Control of the following key, and sub-keys, on the Windows NT computer:
To stop the problem from reoccurring, use Regedt32 to grant the Users group Full Control, using the Security / Permissions menu. Remember to check the Replace Permissions on Existing Subkeys box and to press Yes when prompted to confirm the replacement.
To reclaim the lost licenses, call the Microsoft Clearinghouse.